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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<refentry id="sysctl.d">

<refentryinfo>

<title>sysctl.d</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Lennart</firstname>

<surname>Poettering</surname>

<email>lennart@poettering.net</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>sysctl.d</refentrytitle>

<manvolnum>5</manvolnum>

</refmeta>

<refnamediv>

<refname>sysctl.d</refname>

<refpurpose>Configure kernel parameters at boot</refpurpose>

</refnamediv>

<refsynopsisdiv>

<para><filename>/etc/sysctl.d/*.conf</filename></para>

<para><filename>/run/sysctl.d/*.conf</filename></para>

<para><filename>/usr/lib/sysctl.d/*.conf</filename></para>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para>At boot,

<citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>

reads configuration files from the above directories

to configure

<citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>

kernel parameters.</para>

</refsect1>

<refsect1>

<title>Configuration Format</title>

<para>The configuration files contain a list of

variable assignments, separated by newlines. Empty

lines and lines whose first non-whitespace character

is <literal>#</literal> or <literal>;</literal> are

ignored.</para>

<para>Note that either <literal>/</literal> or

<literal>.</literal> may be used as separators within

sysctl variable names. If the first separator is a

slash, remaining slashes and dots are left intact. If

the first separator is a dot, dots and slashes are

interchanged. <literal>kernel.domainname=foo</literal>

and <literal>kernel/domainname=foo</literal> are

equivalent and will cause <literal>foo</literal> to

be written to

<filename>/proc/sys/kernel/domainname</filename>.

Either

<literal>net.ipv4.conf.enp3s0/200.forwarding</literal>

or

<literal>net/ipv4/conf/enp3s0.200/forwarding</literal>

may be used to refer to

<filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>.

</para>

<para>Each configuration file shall be named in the

style of <filename><replaceable>program</replaceable>.conf</filename>.

Files in <filename>/etc/</filename> override files

with the same name in <filename>/usr/lib/</filename>

and <filename>/run/</filename>. Files in

<filename>/run/</filename> override files with the same

name in <filename>/usr/lib/</filename>. Packages

should install their configuration files in

<filename>/usr/lib/</filename>. Files in

<filename>/etc/</filename> are reserved for the local

administrator, who may use this logic to override the

configuration files installed by vendor packages. All

configuration files are sorted by their filename in

lexicographic order, regardless of which of the

directories they reside in. If multiple files specify the

same variable name, the entry in the file with the

lexicographically latest name will be applied. It is

recommended to prefix all filenames with a two-digit

number and a dash, to simplify the ordering of the

files.</para>

<para>If the administrator wants to disable a

configuration file supplied by the vendor, the

recommended way is to place a symlink to

<filename>/dev/null</filename> in

<filename>/etc/sysctl.d/</filename> bearing the

same filename.</para>

<para>The settings configured with

<filename>sysctl.d</filename> files will be applied

early on boot. The network interface-specific options

will also be applied individually for each network

interface as it shows up in the system. (More

specifically,

<filename>net.ipv4.conf.*</filename>,

<filename>net.ipv6.conf.*</filename>,

<filename>net.ipv4.neigh.*</filename> and <filename>net.ipv6.neigh.*</filename>)</para>

</refsect1>

<refsect1>

<title>Example</title>

<example>

<title>/etc/sysctl.d/domain-name.conf example:</title>

<programlisting># Set kernel YP domain name

kernel.domainname=example.com</programlisting>

</example>

</refsect1>

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>